8 May 1998


WHEN pollution risks are considered nitrogen is usually the key element but phosphorus poses more risk to waterways than previously thought, according to IGER researcher Phil Haygarth.

He estimates that when phosphorus supplies reaching soil through animal manure, slurry and in artificial fertilisers are added, an excess of 26kg/ha of phosphorus is applied annually.

"Of this 3kg/ha can be lost but levels of only 10kg/litre are enough to cause eutrophication and the development of algal blooms which can cause livestock deaths and sickness in humans.

"Legislative controls could, therefore, tighten and phosphorus vulnerable zones may be one option introduced in the long term," says Dr Haygarth.

To pre-empt losses Dr Haygarth urges producers to consider the different ways phosphorus can be transported – such as through soil leaching and run off.

Soil tests may provide a valuable measure of phosphorus present which can aid producers when calculating the amounts of phosphorus to apply. But this does not take account of soil run-off risks.

"Producers must, therefore, cut the likelihood of run-off occurring by considering high risk areas," says Dr Haygarth.

For example, he says that run-off is more likely to occur on heavily poached land and when rain follows applications.

"When these factors are present, applications should be avoided," he warns. &#42

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